Backwash when the pressure gauge tells you

That’s the real answer.

Don’t backwash on a schedule. Backwash when the filter pressure gauge reads 8–10 psi higher than it did right after you cleaned the filter. That’s the only reliable sign.

You’ll see other signs too — slower return flow, maybe the pump sounds different, or the skimmer isn’t pulling as well. But the pressure gauge is the clearest signal. If you backwash by calendar, you’re either wasting water and time (if you do it too often) or letting the filter clog up and stress the pump (if you do it too rarely).

How often that happens depends on your pool — debris load, usage, weather. Could be every few days in peak leaf season, maybe every couple of weeks otherwise. Check the gauge weekly, or after heavy use or a storm.

Trust the gauge, not the calendar.